Aluminum hydride (AlH3), also referred to as “alane,” is an attractive hydrogen storage material for portable fuel cells due to its high theoretical hydrogen storage density when reacted with liquid water (hydrolysis reaction), and its potential for low cost in high-volume production. Pure alane, however, reacts slowly with water (liquid or vapor) due to a passivation layer (oxide) which forms on the grain surface and reduces the diffusion rate of water to the unreacted core. The reaction rate of pure alane with water is too slow to be useful for portable fuel cells.
Recent work by Teprovich et. al. (International Journal of Hydrogen Energy 37: 1594-1603 (2012)) describes that the addition of a promoter additive (PA) such as a metal hydroxide (e.g., NaOH) or metal hydride (e.g., LiH) can improve the reaction rate of alane with liquid water. It is thought that the strongly-basic solution that forms when liquid water is introduced to the alane-PA mixture is able to effectively dissolve the oxide passivation layer that forms on the surface of the alane particles, enabling a higher reaction rate. But the need for liquid water makes systems such as Teprovich's inefficient when one accounts for the weight of the liquid water that must be carried “on board.” There is therefore a need for an alane hydrolysis system that does not require carrying a significant amount of liquid water on board to effect the hydrolysis of the alane.